(1) Field of the Invention
This invention relates to the use of solar energy captured with a solar pond in a warmed brine layer therein, and it also relates to the use of energy recovered by flash-down evaporation from warmed or hot coolant water rejected as waste heat to the environment by power plants, industrial thermal processes, internal combustion engines, and available heat energy contained in liquids. Such energy is also known as latent heat evaporation or of flash-down evaporation. In either case, heat contained in solar heated brine or in another liquid such as an industrial coolant, is converted into steam or vapor having a temperature generally below about 200.degree. F. and above 100.degree. F., but also applicable outside this range, by recovering this heat or part thereof in the form of low pressure steam or vapor by flash-down of the liquid under a vacuum or a partial vacuum. The barometric evaporator provides or improves a process or apparatus, or a procedure to recover such heat, or waste heat, from a warm or hot liquid or brine with a high thermal efficiency, and it also includes use of such steam or vapor for example in desalination or purification of wastewater or seawater, to produce a distilled water product, or for the recovery of energy therefrom e.g. to drive a turbine, or to lift or elevate a liquid phase and to use this lifting effect to provide for subsequent removal of a liquid by gravity from a vessel under vacuum or to discharge it into a pond without using a pump or for recycling it to the heat producing source. This process or method is applied in several related procedures whereby a range of distillate gains is achieved with a range of designs including an evaporator or heat exchanger or a condenser. The steam or vapor produced by flash-down is subsequently condensed into distillate in a heat exchanger, an evaporator or a condenser. The vapor's heat of condensation thus liberated may be used in a single effect vertical tube evaporator (VTE) or in a multi-effect (ME) series of vertical tube evaporators (ME-VTE) to increase the distillate product, or to increase the gain ratio of distillate produced to steam used. Substantial additional flash-down of the original hot liquid may be applied in or immediately prior to each evaporation step in such a ME-VTE series, to thus increase significantly the thermal flux and the amount of heating steam applied in each next step of such a step-wise series of evaporators, and to increase the distillate capacity per effect. This increase in thermal flux effect-to-effect in part distinguishes this ME-VTE series from a conventional multi-effect series of vertical tube evaporators.
(2) Description of the Prior Art
In the multi-stage flash evaporation (MSF) process for the desalination of seawater or its brine concentrate, the feed is first preheated stage-to-stage with vapor and then with steam to a high temperature of up to about 220.degree. F., and the feed is then flashed-down horizontally stage-wise to lower temperatures stage-to-stage as the residual brine concentrate passes through inter-stage gates to the reduced pressures maintained in the series of stages, and by releasing vapors that preheat the feed. The lowest stage temperature depends on the coolant used, and is usually close to and above the coolant temperature. The number of stages applied may vary, usually within a range of 16 to 90, and the flash-down range is usually only a few degrees, up to about 5.degree. F. Each stage is typically an rectangular vessel, and one of an in-line series by subdividing an elongated horizontal vessel into separate stages with submerged brine flash-down gates dividing these stages. The vapor produced by flash-down is condensed on a horizontal bundle of heat exchanger tubes extending through the stages conducting the feed liquid or seawater being gradually heated stage-to-stage as it passes counter-current to the direction of flash-down brine flow. This feed is then further heated with steam (e.g. to 220.degree. F.) in a feed heater before it is turned around and enters the first flash-down stage in the MSF series and flashes down while cooling the residual brine stage-to-stage. In this process the stages are usually in a horizontal series, and the final brine concentrate as well as the accumulated condensates or distillates are pumped out from the vacuum maintained in the last stage and discharged at ambient pressure or above it.
In conventional multi-effect (ME) upflow or downflow vertical tube evaporation (VTE) of seawater or brine; the evaporator effects are fed in series with the feed liquid and partial concentrates or residual feed, and the heat flux is usually about equal in each effect, and they usually have an equal number of tubes or equal tube surface areas per effect. Flash-down of the feed is then controlled by the available effect-to-effect temperature difference (.DELTA.T) and the tube-side pressure drop in each effect. The effect .DELTA.T usually ranges from about of 3 to 8.degree. F. at the high temperature end or first effect to about 6 to 16.degree. F. at the low temperature end or last effect; this range is imposed by effect thermal efficiencies (or overall heat transfer coefficients), and by the thermal efficiency in the first effect being about twice that in the last effect.
The use of power plant turbine exhaust steam for evaporation of seawater and power plant wastewater by vertical tube evaporation (VTE) has been reported, for instance in U.S. Pat. No. 5,156,706 which is about the useful application of low temperature waste steam, such as turbine exhaust steam, being available under vacuum. The present disclosure is about producing steam from warmed wastewater or hot brine by flash-down under reduced pressure, and about using such steam for desalination or water purification or wastewater concentration by vertical tube evaporation.
The use of an adjustable orifice plate for the control of feed flow and flash-down thereof as the feed flows into a bundle of vertical evaporation tubes in the down-flow mode, is disclosed in U.S. Pat. No. 5,968,312. A similar or partially similar adjustable orifice plate is applied in the present disclosure for the purpose of controlling upflow feed flow with flash-down and the continued evaporation of the residual feed within a channel with the objective of bringing the vapor and residual feed flows to thermal equilibrium or close thereto during co-current or continuous parallel flow of these phases along the length of such flash-down channels.